1. Field of the Invention
The present invention relates to a magneto-optical memory device, wherein information is recorded into, read out from, or erased from a recording medium by applying a laser beam onto the recording medium having a magnetic thin-film recording layer. The present invention relates, more particularly, to an optical system in a magneto-optical memory device.
2. Description of the Prior Art
Recently, an optical memory system has been developed, which ensures high density storage, large storage capacity, and high speed accessing. In particular, an optical memory system is provided wherein a row of fine pits are formed in a recording medium and the diffraction effect of the light beam at the pit portions is used for reproduction purposes, or another optical memory system wherein bit shaped areas having a different refractive index are formed in a recording medium and the variation of the refractive index or transparency is used for reproduction purposes and has practical application. However, the optical memory system can only perform the reproduction operation, or perform add-on recording at best. That is, the conventional optical memory system can not perform the erase operation which is one of the most remarkable features of the present memory system.
A magneto-optical memory system has been developed, which includes a recording medium made of magnetic material. The magneto-optical memory system is very effective because the recording/erasing operation is easily conducted in the magneto-optical memory system. However, the conventional magneto-optical memory system can not ensure the high quality of the reproduced signal, and the optical system thereof is complicated.